Field
This invention relates generally to electronic circuits, and more specifically to amplification of signals in low power consumption circuits.
Related Art
Low power consumption circuits (circuits consuming less than 5 μW) that amplify a small magnitude voltage typically use resistors that have very high ohmic values to maintain low currents. Examples of such low power consumption circuits are low-power voltage reference circuits and low-power temperature sensor circuits. A bandgap voltage reference circuit is a temperature-independent voltage reference circuit that outputs a fixed DC voltage at or near a bandgap voltage of a semiconductor substrate on which the voltage reference circuit resides. The extrapolated bandgap voltage of silicon at zero kelvin is 1.22V.
With most low-power bandgap voltage reference circuits, there is a need to amplify a small signal of a few to tens of millivolts into a larger signal of several hundreds of millivolts. In some known low-power bandgap voltage reference circuits, the small signal that is amplified is a proportional-to-absolute-temperature (PTAT) voltage. If resistors are used in such known circuits, a drop of several hundreds of millivolts across the resistors is needed, which requires resistors having values in the range of tens of megaohms so that the current is limited to nanoamps. Such high ohmic value resistors occupy very large areas, which result in high area cost and/or impose a minimum power constraint. This unfavorable power/area trade-off usually determines a minimum power that can be obtained at an acceptable area cost.
Several low-power bandgap voltage reference circuits that do not use resistors, and instead use metal-oxide-semiconductor (MOS) transistors, are known. However such known circuits do not provide sufficient linearity because of the presence of various error sources such as second-order effects. Furthermore, such known circuits are subject to fabrication process and spread. Also, such known circuits require extensive trimming. Consequently, such known circuits are much less accurate than conventional bandgap voltage reference circuits that employ resistors.